1. Field of the Invention
The present invention relates to graphite-containing refractories having high endurance.
2. Development of the Invention
Graphite-containing refractories have been employed for many years in various fields including the steel making industry. It is known that graphite-containing refractories are characterized by properties such as high thermal conductivity, high resistance to thermal stress, and resistance to wetting by various molten slag. Recently refractories fabricated by blending graphites with a variety of oxides, nitrides, carbides or the like have been widely employed. A rapid increase has been noted in the use of such refractories particularly for lining the bottom of blast furnaces, torpedo cars and converters and, other major parts such as nozzle stoppers and slide closure devices for flow control, nozzles for a continuous casting process, and the like. Representative examples of the refractories include alumina-graphite, used for a continuous casting nozzles and magnesia-graphite, used as a lining of converters, etc. In the past, materials such as fused silica and the like have been employed but recently alumina-graphite, which has excellent resistance to corrosion, has become the standard. Further, products obtained by duplex simultaneous molding process where a slag line portion is reinforced with zirconia-graphite have come into use. Such refractories exhibit excellent endurance.
However, because the requirements for improving the quality of steel have become severe with the progress in the continuous casting process, excellent endurance has been more strongly desired.
The need for improving the endurance has also involved the latter magnesia-graphite refractories.
In addition, an importance of graphite-containing refractories has recently been increased since it is found that such refractories can be used as the material for introducing gas or powders into molten steel while having the improved resistance to corrosion and improved mechanical properties.
The wear process of these graphite-containing refractories is generally considered as follows: Firstly, the organic binders which as used in blending operation are carbonized to form carbon. Such carbon and graphite present in a refractory blend disappear due to oxidation or dissolution into steel. Accordingly, the structure of the working surface of the lining becomes loose, and is worn out receiving the severe flow of molten steel. Several countermeasures such as reduction of graphite amount, reinforcement of the structure with fine particulation of aggregates and careful selection of graphite raw materials, improvements in resistance to oxidation and resistance to penetration of molten steel, etc. have been worked out. These countermeasures assisted in prolonging the life. However, the improvement is still moderate and therefore less than optimal.